Immunohistochemical localization of the oestrogen-responsive 110 kDa and 74 kDa polypeptides and complement component C3 in the rat genital tract after oestrogen treatment and during the oestrous cycle.

In previous studies we showed that two oestrogen-responsive rat uterine secretory polypeptides of molecular mass 110 and 74 kDa share sequence similarities with the alpha and beta chains of rat complement component C3. Using polyclonal antibodies specific to the 110 kDa polypeptide, the 74 kDa polypeptide and rat serum C3, we studied the localization of these proteins in the rat genital tract using an indirect immunoperoxidase technique. The results showed that in oestradiol-treated rats immunostaining for the three antigens was heterogeneously distributed in the epithelia of the endometrium, cervix and vagina and that the intensity of staining was greater after oestrogen treatment than in controls. In oestradiol-treated immature rats, the immunoreactivity for the 110 kDa and 74 kDa polypeptides was greater in the endometrial and vaginal epithelia than in the cervical epithelium, whereas immunoreactivity for C3 was greatest in the vaginal epithelium. In cyclic rats, staining by all three antibodies was seen only during pro-oestrus and oestrus, during which stages the immunostaining for the 110 kDa and 74 kDa polypeptides was detected only in the endometrial epithelium, whereas immunostaining for C3 was also found in the epithelia of the cervix and vagina. In general, consecutive sections of these tissues revealed a close correlation between the immunostaining for the 110 kDa and 74 kDa polypeptides and C3. However, there were some sections that showed clear differences in staining, suggesting that more than one C3-related protein species was detected in the female rat reproductive tract.